UPPERCASE causes all lower-case characters to be converted to uppercase in symbols and opcodes. This does not affect characters used in strings. NOUPPERCASE allows symbols using upper- and lower-case to be considered differently. For example, ABCD and abcd are different symbols if NOUPPERCASE is in effect. All assembler keywords and opcodes can be any combination of upper- and lower-case. Thus, NOP, nop, and NoP are all recognized as an opcode, regardless of the state of this control.